Development of methods for storage of electrical energy has become highly important in recent time. Two main general approaches for reversible storage of electric energy are commonly used. The first one is supercapacitors, where energy is stored in the form of an electric double layer. In the second approach, the energy is stored in the form of chemical energy in rechargeable batteries. While the supercapacitors allow higher power density, the rechargeable batteries are able to provide higher energy density. Among all variety of rechargeable batteries, ones based on lithium deserve particular attention. In fact, lithium is the lightest metal and has the highest oxidation potential among the metals that allows much higher energy density comparing, for example, to Ni—Cd rechargeable batteries. Currently, Li-ion batteries based on LiMnO2 and LiCoO2 cathodes are practically used. These Li-ion batteries provide good cycling and very high Coulombic efficiency. On the other hand, they suffer from insufficient energy density. For example, the distance which can be traveled by a car equipped with a Li-ion battery is about 50-160 km, which in many cases is insufficient for everyday use. Li—S batteries are the emerging class of rechargeable batteries, which potentially can provide much higher energy density. Although the lithium-sulfur system operates at a comparably low average potential of 2.1 V against Li+/Li, it shows a high theoretic specific energy of 2600 Wh/kg due to the extraordinary theoretical specific capacity of 1675 mAh/gs (gs stands for per gram of sulfur).
The essential element of Li—S batteries is the sulfur cathode. Sulfur itself is electrically insulating and therefore composite cathodes, which consist of sulfur and porous conductive materials such as carbon, are used. Different carbon materials including acetylene black, carbon nanotubes, graphene, CMK-3 and microporous activated carbon fibers were used as conductive component. Typically, these carbon materials are powders, which consist of grains with certain size. The porosity of these materials is controlled by the size of the grains and internal porosity of the grains. Very recently, polymers were introduced as precursors for design of porous carbon cathodes. Due to their flexibility, polymers may be used for fabrication of carbon materials with various micro and nano-morphologies. For example, carbonization of polyacrylonitrile (PAN) mixed with Na2CO3, poly(methyl methacrylate) (PMMA)—PAN blends, polymer; fibers prepared by electrospinning, polypyrole, sucrose, formaldehyde-phenol resin mixed with tetraethyl orthosilicate were used to prepare porous carbon cathodes. Due to interconnectivity of pores and carbon phase as well as large surface area, opal and inverse-opal⋅structures deserve particular interest as candidate for possible carbon structures. For example, Schuster, J.; He, G.; Mandlmeier, B.; Yim, T.; Lee, K. T.; Bein, T.; Nazar, L. F., Spherical Ordered Mesoperaus Carbon Nanoparticles with High Porosity for Lithium-Sulfur Batteries, Angewandte Chemie, International Edition 2012; 51, (15), 3591-3595 disclose fabrication of opal-like porous carbon structure using PMMA particles as template, which was filled with SiO2 and PMMA was replaced by CMK-3 carbon. Inverse-opal like carbon structures were also prepared by carbonization of poly(furfuryl alcohol) and demonstrated very good cycling properties.